egl: fbdev: Allow multiple eglGetDisplay() calls

We don't support multiple windows but if the previous window has been
dealt with there is no reason why starting from scratch with eglGetDisplay()
would not work.

Signed-off-by: Kalle Vahlman <kalle.vahlman@movial.com>
Merge pull request #147 from kvahlman/fdev-multidisplay

egl: fbdev: Allow multiple eglGetDisplay() calls